Peripheral component interconnect (PCI) is a common industry input-output (I/O) structure for connecting a selection of functions to a device, such as a computer, to tailor the system to the users requirements. The PCI bus provides a state of the art, industry standard high data rate, design of choice for many applications. PCI cards, used for attachment to the PCI bus, come in three types: +5 volt boards, +3.3 volt boards and dual voltage signaling boards. The systems that accept these cards can only power two types, +5 volt boards and dual voltage boards or +3.3 volt boards and dual voltage signaling boards. This because the signaling voltage (Vio) is fixed on the PCI card backplane to +5 volts or +3.3 volts, and the PCI connectors are keyed to accept only a card capable of using the hard wired voltage.
The environment wherein the PCI connectors that attach PCI cards to the PCI bus are of two keyed types, for either +3.3 volt or +5 volt cards, is not a problem when the connector is to receive a known voltage PCI card. However, when connectors are provided for future cards or optional function cards to be subsequently selected, the device designer must select the type of connector or the mix of connector types to be used. The connector selection can be further complicated since in the future the use of +3.3 volt cards is expected to be more prevalent than the currently more extensively used +5 volt cards.